1. Field of the Invention
This invention relates to the production of a helical band that can advantageously be used to form a helical flange on an insulator in an overhead electric power transmission line.
With high-voltage and extra-high-voltage transmission lines, the line conductors are generally supported by lattice steel towers, or pylons, via suspension type insulators able to carry loads of up to 10 tons or more. These insulators are designed to minimize current leakage and prevent surface flashover in rain and fog or under conditions of atmospheric pollution. For safe operation, the insulators should define leakage paths between the ends thereof that are as long as possible in relation to the axial length of the insulators and of uniform width, as can be achieved with helically arranged flanges.
2. Prior Art
Such insulators have long been produced with helical flanges around a cylindrical core. German Patent Specification No. 1190072 of Apr. 5, 1963 describes how to form such flanges on a core-forming cylindrical rod. French Patent Specification No. 76.25859 of Aug. 26, 1976 describes a flange made of plastic material. Neither of these prior specifications show how to produce such a flange. In German Patent Specification No. 2905874.0 of Feb. 16, 1979 applicant describes a method of producing a band of plastic material between a pair of heated conical rollers and for applying the band to a substantially cylindrical rod of electrically insulating material to form an insulator with a helical flange.